THE SIR SUPPLIED DR. FEINBERG WITH 2.5G OF S-BENZYL-L-[13-2H2] CYSTEINE. THE IRON-SULFUR CLUSTERS OF TETRANUCLEAR IRON-SULFUR PROTEINS AND ENZYMES TYPICALLY HAVE FOUR CYSTEINES (CYS) AS LIGANDS, I.E. [4FE-4S]CYS. AN EXCEPTION IS D AFRICANUS FERREDOXIN (DA FD), WHICH HAS AN ASPARTATE AS ONE LIGAND. THE [2FE-2S]RIESKE PROTEINS APPARENTLY HAVE TWO HIS RESIDUES AS LIGANDS. THE ASPARTATE OF DA FD HAS NOT BEEN PROVEN TO BE AN EFFECTIVE OR REAL LIGAND. ADDITIONALLY, AND AS A SEPARATE RESEARCH GOAL, WHILE MOST FD WORK HAS BEEN DONE WITH CLOSTRIDIUM PASTEURANUM FD, ITS STRUCTURE HAS NOT YET BEEN DETERMINED. BY USING 3-13C CYSTEINE AND 3-13C ASPARTIC ACID WE WILL BE ABLE TO MAKE SIGNIFICANT PROGRESS ON BOTH THESE PROBLEMS. IN REGARD TO THE NATURE OF THE LIGANDS, WE WILL STUDY THE EXTENT OF CONTACT SHIFTING OF 13C NMR SPECTROSCOPIC RESONANCES OF FDS WHICH ARE PREPARED BY SITE SPECIFIC INSERTION OF 3-14C CYS AND 3-13C ASPARTATE INTO TOTALLY SYNTHETIC FD APO-PROTEINS WHICH ARE THEN RECONSTITUTED TO THE HOLO FDS. IN ADDITION TO THIS WORK, WE HAVE EMBARKED ON A COLLABORATION WITH PROFESSOR IVANO BERTINI, UNIVERSITY OF FLORENCE, ITALY, ON THE COMPLETE NMR SPECTROSCOPIC DETERMINATION OF THE 3D STRUCTURE OF CP FD. THE PREPARATION OF "NAIVE SEQUENCE" SYNTHETIC PROTEIN IN WHICH ALL OR SOME OF THE EIGHT CYS HAVE BEEN REPLACED BY THE 3-13C CYS WILL PERMIT ADDITIONAL NMR PULSE FORMATS TO BE USED, WHICH IN TURN WILL FACILITATE THIS 3D NMR STRUCTURE DETERMINATION.